This invention relates to the additive compositions, also known as admixtures, for incorporation in hydraulic cement mixes, and more particularly to additive compositions for use in dry mixes, such as those used in making masonry units, pipe and the like.
Non-plastic, dry concrete mixes, in which the amount of mix water is minimized, are used in the manufacture of concrete block, concrete pipe, and other concrete products and structures. Although these dry mixes contain portland cement, aggregate, and water, there is a substantial difference between such concrete mixes and conventional mobile or plastic concrete mixes. The problems involved in the use of non-plastic dry mixes are different from those encountered in the use of conventional concrete mixes, since the dry mixes contain only a minimum of water instead of the larger quantities of water employed in the plastic concrete mixes to give mobility and flowability.
Additives developed for use in plastic concrete mixes are often inapplicable or unsuitable for use in non-plastic dry concrete mixes. For example, there are many well-known additives used as water-reducing and plasticizing agents in plastic concrete mixes. Such additives would not be applicable for these purposes in dry concrete mixes because water reduction and plasticizing are not generally relevant to manufacturing dry mix masonry units.
Another area in which the technology of dry mixes differs from that of plastic mixes is in the problem of air entrainment. Additives used as air-entraining or air-detraining agents in plastic mixes may have little or no utility in dry mixes. Conversely, additives which may be suitable for use in dry mixes may be unsuitable for plastic mixes because of adverse effects on air entrainment in such mixes.
Additives which can increase the strength of masonry units produced from a given dry concrete mix, or which allow the reduction in the amount of cement in such mixes to produce a unit of a given strength are highly desirable. Yet the use of additives for the plastic concrete industry as additives for harsh, relatively dry concrete mixes has not been entirely satisfactory for a number of reasons. First, these additives frequently are simply ineffective in substantially improving the strength of the dry concrete products. In addition, such additives often do not improve or have deleterious effects on other factors which are special to dry mix production but inapplicable to plastic concretes.
One such factor which is of importance in masonry unit production which is irrelevant in the plastic concrete art is friction between the dry mix and the molds and forms through which it must be forced during the production process. When the friction is high it takes more time to force the mix into the molds and forms, thus increasing the manufacturing time per unit, known as the "cycle time." Furthermore, increased friction results in increased abrasive wear on the equipment surfaces which are in contact with the dry mix, causing increased equipment costs and production delays. Therefore an additive which can increase the lubricity of the dry mix with relation to the production equipment is highly desirable, and an additive which may increase strength but which may have a deleterious effect on lubricity might not be suitable for use in dry mixes.
Another problem in the masonry unit industry, particularly with block, has been the lack of uniformity of surface texture and color both with respect to the surface of an individual unit as well as the lack of uniformity from one unit to another which becomes apparent when units are placed together in a wall or other structure. Also, in the case of concrete block, the consumer generally prefers block of lighter shades of color and those having a wavy textural effect known in the industry as a "water-webbed effect". Although it is sometimes possible to produce concrete block with a fair degree of uniformity as far as the surface of an individual block is concerned, it has been extremely difficult, if not impossible, to regularly achieve a high degree of uniformity both as to the surface of an individual block and particularly from one block to another over an extended period of commercial operation. Attempts have been made to produce a pleasing surface texture on the block or other molded masonry units by the use of an additional amount of water in the mix. However, this has not proven successful since the additional water may give the surface a smeared appearance and, in addition, may create problems in the molding and processing of the block.
Many of the additives which have been used to increase strength in plastic concretes have been found unsuitable for use as dry mix additives because of deleterious effects on surface characteristics and color. Therefore, to be suitable for dry mix use, an additive should also produce masonry units with a pleasing appearance and light color.